The manufacture of glass involves the heating of glass batch materials to high temperatures (approx. 1500.degree. C.) in order to melt and homogenize the various constituent components. This process is generally carried in furnaces heated directly by the combustion of some sort of fossil fuel. By far, the most common type of glass manufactured is termed soda-lime glass, used for windows, tableware, bottles, etc. This glass is characterized by its batch material, consisting primarily of silica sand, limestone, soda ash and salt cake. The present invention is concerned primarily with this glass type, but other glass types, such as borosilicate, aluminasilica, lead, etc., also lie within the scope of the invention.
Particulate emissions from glass furnaces consist primarily of submicron condensates of alkali metal sulfates that result from a combination of a gas such as sulfur oxide and an alkali metal such as sodium. To a lesser extent, potassium is also present in furnace exhaust gases. Collection and handling of these particulates is made difficult because of their low bulk density, hygroscopic tendency, and acidic potential. The gaseous emissions of primary concern are sulfur oxides. These are derived primarily from sulfur materials added with the glass batch (salt cake) and from sulfur in the fossil fuel used to heat the furnace. The bulk of the emissions are in the form of SO.sub.2, but a significant portion are in the form of SO.sub.3. Other pollutants which may be present depending upon the specific glass type are boron, fluorine, chlorine, and lead oxide dust. Reduction of all these emissions are being mandated by increasingly stringent government regulations.
A recent development in pollution control is electrostatic granular bed filter (EGB) technology, as exemplified by U.S. Pat. No. 4,338,113. Pollutants are adhered to electrically charged granular material as exhaust gases pass over the granules.
This technology has been found to be very effective in removing pollutants. However, a problem occurs in that over a period of time, the conductivity of the granules increases, which correspondingly decreases their ability to trap pollutants. This greatly reduces the useful life of the granules and necessitates down time to replenish the granular bed with fresh material. Hence, while EGB technology provides effective pollution abatement, there remains a need in the art for prolonging the useful life of granules used in EGB technology.